This invention relates to gas generators suitable for filling inflatable structures in the presence of humans. It has specific application to passive restraint cushions designed to provide impact protection to occupants of automotive vehicles.
The various degrees of violence experienced in automobile collisions make it impractical for a safety cushion to respond to all such situations with a fixed inflation level. An example of the extremes encountered would be the case of a large man in a high "g" impact and that of a child standing adjacent to the bag in a low level crash. A safety cushion forceful and fast enough to provide the support necessary to protect the large man in the high "g" impact deploys with such velocity that it would constitute serious risk of injury caused by rebound or rearward acceleration to the standing child in the low speed impact.
Attempts to solve this problem have been made in some current passive restraint systems by using a two level, pyrotechnic augmented, compressed gas bottle and a two level sensor. The sensor responds to the severity of impact by sending appropriate signals to fire one or both pyrotechnic charges. The burning pyrotechnics add heat to the stored gas and reduce the requirement for the quantity of gas that must be stored. The quantity of pyrotechnics being burned simultaneously determines the gas temperature and volume and resultant bag inflation level. An explosive charge ruptures a diaphragm at the orifice of the bottle.
This system, however, has been found to be unsatisfactory for a number of reasons: (1) The presence of an explosive charge at the orifice of the gas bottle and pyrotechnic charges inside the bottle of high-pressure gas makes this system somewhat hazardous to handle, ship, and store; (2) The system tends to be somewhat complex and bulky; and (3) The volume of gas and speed of its delivery to an inflatable structure is somewhat influenced by the initial temperature of the gas bottle -- if it is initially very cold, the rate of inflation tends to be slowed.
A second two-stage system is shown and described in U.S. Pat. No. 3,663,035 to T. W. Norton, titled "Self-Contained Passenger Restraining System" (FIGS. 7 and 8). In this system, the main gas generating material is black powder; and, to avoid inflating the cushion with explosive force, the gas generant material is divided into two stages -- one of which is delayed slightly by a time-delay fuse. This system is not intended to be responsive to variations in violence of impact on collision of the vehicle with another object; it is simply a means of using materials that are almost explosive to inflate a safety cushion.